I propose to investigate the mechanisms by which vasoconstrictor hormones (angiotensin II, vasopressin, Alpha-adrenergic agents) stimulate calcium and prostaglandin (PG) biosynthesis in cultured rat mesenteric arterial smooth muscle and endothelial cells. The following are specific questions to which answers may be elicited: a) Do vasoconstrictors alter cytosolic calcium levels in cultured cells as measured directly by photoprotein luminescence or fluorescence of intracellular organic calcium indicators? b) What is the role of intracellular and extracellular calcium in hormone-evoked PG biosynthesis? c) What are the effects of vasoconstrictors on the metabolism of phosphatidylinositol, phosphatidic acid and polyphosphoinositides? What is the role of calcium in mediating these changes? d) Does phosphatidic acid function as an endogenous cellular calcium ionophore? e) Do polyphosphoinositides function as endogenous intracellular calcium stores? We expect to use the following analytical techniques to achieve our goals: radioimmunoassay of PGs, measurement of intracellular calcium by a novel technique of aequorin luminescence (or alternatively, measurement of intracellular calcium with the aid of intracellular fluorescent calcium indicators), transmembrane flux of radio-active calcium and radiometric thin-layer chromatography of phospholipids. The results obtained from this research program may increase our understanding of the role played by phospholipids in regulating calcium channels and of the role played by calcium in regulating PG biosynthesis and vasoconstriction.